A known machine of this type comprises a pickup device extended by a large guide surface with which a drive element (disks or routing screws) cooperates. The guide surface consists of a curved plate at least partially in the shape of a helix and rising toward the back. During work, the pickup device routes the hay on the curved plate. This hay is taken up by the drive element, which is essentially oriented in the direction of the flow of the hay conveyed by the device. The drive element then moves the hay toward the back of the plate and causes it to fall back on the ground. During this movement, the curvature of the plate is supposed to cause a flipping over of the hay to obtain the desired turning over.
On this machine, the surface of the plate is larger than the action zone of the drive element. Accordingly, accumulations of hay occur in places located outside the the action zone. These accumulations quickly cause disturbances in the movement of the hay and can even cause obstructions or, indeed, total blocking of the drive element.
Additionally, the guide surface of the curved plate must be very large to assure a complete turning over of the hay. Because of this, the prior art machine is heavy, bulky, and, consequently, difficult to handle.